Hardware part do not have big issue now, just pin 9, 10 are the microSD detector pin, but there is no place on PCB, have to ignore them…

Now working on the software part, that really stunned me. 😀

I thought that should be already perfectly supported by openwrt driver…But after I check the  driver carefully, I think I have to modify that code or find another way.

The code is under linux kernel source, source/drivers/mmc/host/mmc_spi.c

There is a note in that source…

 58  * - MMC depends on a different chipselect management policy than the
 59  *   SPI interface currently supports for shared bus segments:  it needs
 60  *   to issue multiple spi_message requests with the chipselect active,
 61  *   using the results of one message to decide the next one to issue.
 62  *
 63  *   Pending updates to the programming interface, this driver expects
 64  *   that it not share the bus with other drivers (precluding conflicts).

Does that mean this driver can not work with the exists SPI flash?

And there is a good solution but for other router chip.
http://wiki.openwrt.org/ru/toh/tp-link/tl-mr3420/deep.mmc.hack
I did not try that yet, it might be able to work on RT5350 but need more checks.

I do not want to use GPIO for this, but this way looks much easier.
http://wiki.openwrt.org/doc/howto/mmc_over_gpio

This part will cost some time 🙂

Any idea is welcome here. Please leave a comment, that will help a lot. 🙂